Cathode ray tube



Feb. 17, 1942. E, BRUCE 2,273,433.

CATHODE." RAY TUBE Filed April 10, 1940 FIG. 2

IN VE N TOR E BRUCE Patented Feb. 17, 1942 CATHODE RAY TUBE Edmond ,Bruce, Red Bank, N. J assignor to Bell Telephone Laboratories,

Incorporated, New

York, Y., a corporation of New York Application April; 10, 1940, Serial No. 328,816

12 Claims.

This invention relates tocathode ray devices and particularlyto a cathoderray tubehaving a so-called current window in the beam-receiving end thereof.

An object of the invention is to provide acathode ray tube having a current window in the form of a single sharp line: an electron current slit,

.. A further object is to provide a low resistance path ,for the beam current to the exteriorof the tube.

zStill another-object is to provide means for concentrating a maximum of beam current energy-into a single sharp line in the direction in which beam scanning takes place.

There are many connections in which it is desirable to draw current of an electron beam directly outthrough the beam-receiving end of a cathode ray tube, Electrostatic recording as described in U. S. Patent No. 2,200,741, May '14, 1940, to Frank Gray, provides an example. -Another example is provided by a facsimile signal reproducing or printing system which the beam current passes through a current window and through a tape of electrosensitive material to an external electrode,- leaving impressions on the tape which are-proportional to the intensity of the beam current and inversely proportional to the scanning speed. Such a system is described andclaimed in application Serial No. 331,716, filed April 2.6, 1940, of E. Bruce and W. -S.

Gorton.

The well-known Lenard window of thin metal foil has long been used as a means of egress for the beam current from a cathode ray j tube, but, .asidefrom the structural difliculties which attend the supporting of thin metal foil against theiorce of atmospheric pressure over any considerable area, a window of this character ,sufiers from the excessively high attenuation which it offers to the beam current and the consequent reduction in efficiency of the device as a whole.

It has already been proposed to substitute for the well-known Lenard window a mosaic of discrete conductors, each insulated from all the others, and passing through the wall of the beam-receiving end of the tube, perpendicular thereto and substantially parallel with the direction of the oncoming electron beam. Such a mosaic structure is illustrated in Sabbah 'et al. Patent 2,015,570, September 24, 1935. Aside from the serious difiiculties which attend the construction of a current window of this form, it does not lend itself to the uses for'which the tube of this invention was devised and which require a long narrow window'in the form'of a fine, sharp line and constituting in effect an electron current slit. Even if only a single row of the wires of this mosaic were scanned in one direction only in accordance with the scheme'of the aforementioned application, Serial No. 331,716, filed April 26, 1940, thereby sacrificing the great majority of the conductors, it would i still be necessary to focus the cathode beam with excessive sharpness into a minutespot; to focus it, in fact, on the inner end of a single one of the wires of the mosaic. When the cathode beam carries any considerable amount of energy this places an excessively heavy burden on the electron focusing means and presents a problem which, if possible, it is better to avoid thanto meet.

The tube of this invention may comprise a current window of novel form, construction and arrangement which 1meets the objections to the Lenard window and the mosaic, and provides a narrow electron current slit 9 of low electron resistance and through which greatly increased energy may be drawn. .It is characterized in its preferred embodiment by a plurality of closely spaced discrete conductors arranged in a single row, extending through the end wall of-th tube, each insulated "from .all the others. In a preferred modification the individual conductors are disposed in a plane oblique to the direction of the oncoming-electron beam.

The invention in its various aspects will be more fully understood from the following description of preferred embodiments thereof taken in connection with the appended drawing ,in which:

Fig. 1 is aschematic plan view of a cathode ray tube according to the invention;

Fig.2 is a schematic side elevation ofthe tube of Fig. 1 arranged to produce impressions on a sensitized tape, and showing, additionally, simple circuit connections for energizing the tube:

Fig. 3 shows abeam-rficeiving member of the tube of Figs, 1 and 2 to an enlarged scale before its. incorporation in the tube wall; and

Fig. 4 shows one end of the member of Fig. 3 to a still more highly enlarged scale. Referring now to the figures, Figs. .1 and 2 show a closedglass vessel I. having a neck portion 2 and a beam-receiving portion 3 which is enlarged in one dimension .andflattened out into the formof a blunt wedge in the other dimen- $1,011.": An electron gun including a cathode 4, an apertured screen anode 5, an accelerating electrode I, and a pair of beam-deflecting plates 8, 9 are mounted in the neck portion 2 of the tube, and the path of an electron beam I originating at the cathode I, defined by the aperture 6 of the anode and deflected by an electric field between the deflecting plates 8 and 9 is indicated by broken lines.

Mounted in the end wall of the beam-receiving end 3 of the tube are a plurality of closely spaced discrete conductors I2 of minute cross-section which protrude through the wall of the tube, from the inside to the outside, each conductor being insulated from its neighbors. As more clearly shown in Fig. 2, the discrete insulated conductors l2 are arranged in a single row to form a comb. Further, as shown in Fig. 2, they are mounted obliquely to the direction of the oncoming cathode beam I0 so that, despite the minute cross-section of each particular conductor I2, the cathode beam III will strike it at a greater or less distance from the point at which it passes through the tube wall, even though the focusing of the cathode beam ID in a direction perpendicular to the scanning direction be more or less imperfect.

For use of the tube as a facsimile reproducer, the distance from the center line of each conductor to the center line of an adjacent conductor should preferably be not greater than the width of a single picture element to be reproduced; for example, the distance may be of the order of 0.01 inch.

The current window comb of this invention may be formed and incorporated in the beamreceiving end 3 of the tube in any desired manner. For example, it may be formed by plating a glass prism I4 having a bevelled edge with a film of some tough, highly conductive metal, such as platinum, and subsequently subdividing the resulting metal film into a plurality of discrete parallel strips, as by scribing closely spaced lineS through the film. According to another method, the comb may be formed by first masking a plurality of closely spaced parallel strips of the prism surface, then covering the unmasked parts as by plating or sputtering, and finally removing the masking material.

After the plating operation has been completed, the resulting block, bearing its ribbonlike conductors I2, may be sealed into the wall of the beam-receiving end 3 of the tube, bevelled edge outward and with each conductor I2 extending through the tube wall and lying at an angle to the direction of the oncoming electron beam II].

The plating is not limited to one side of the prism. By plating at least two adjacent sides an additional advantage is secured, namely, each conductor turns through an angle inside the tube so that even if the main portion extends through the wall in a direction parallel with that of the oncoming beam, the shorter portion of the same conductor still extends through a substantial distance in a direction perpendicular thereto, so that the beam need not be focused with perfect exactness in the plane of the main portion of the comb. This construction is shown in Fig. 4.

Indeed, all four sides of the prism may be plated,

if desired, and the lines of separation continued all the way around the prism so that each conductor consists of a loop. This loop may be continuous, or, if desired, all of the loops may be severed at their outer ends by grinding, thus providing U-shaped conductors, the bend of the U being inside the tube. For certain purposes, for

example the purposes fully described in the aforementioned copending application Serial No. 331,716, filed April 26, 1940, in which a sliding contactor bears against certain of the conductors of the comb, the return side of the loop may be of decided advantage. In any event, it may be used as a spare in case of injury to the main or working portion of the same conductor.

The inner surface of the beam-receiving end 3 of the tube is preferably coated with some conductive substance I6 such as that commonly known as aquadag, and it is advantageous to spread some high resistance fluorescent material I5, such as zinc silicate, on the glass surfaces between and adjacent to the comb wires I2 inside the tube to enable focusing to be adjusted visually. This is indicated in Fig. 4 which shows one end of the glass prism with the discrete ribbon-like conductors I2 applied thereto and fluorescent material I5 between them.

Fig. 2 shows circuit connections for the tube of this invention when incorporated as a component part of a facsimile printer. The negative terminal of a battery 20 or other source of potential is connected to the cathode 4 and the positive terminal to the beam-defining anode 5. The negative terminal of another battery 2I is connected to the anode 5 and the positive terminal to a knife edge 22 which is placed in close parallel alignment with the outer ends of the comb wires I2 and also, through a resistance 24, to the accelerating anode 1. An appropriately sensitized low resistance paper tape 23 is arranged to be advanced between-the comb wires I2 and the knife edge 22 by a suitable mechanism, not shown; and the cathode beam I0, originating at the cathode 4, may be swept along the row of comb wires by a scanning voltage of suitable wave form impressed on the deflecting elements 8, 9 in any desired manner. For example, the scanning may be either oscillatory or at constant speed with rapid fly-back or at variable speed in accordance with the so-called "velocity modulation system.

The conductive lining l6 of the tube is connected through the resistor 24 to the positive terminal of the battery 2| to withdraw stray electrons, especially secondary electrons which may be driven out of the comb wires by impact of the primary electrons of the cathode beam and which might otherwise modify the motions of the primary electrons in an objectionable manner.

It will be understood by those skilled in the art that current flow may take place from the outer point of that particular conductor I2 of the comb which is instantaneously impinged by the cathode beam to the knife edge 22 which is placed close thereto on the far side of the sensitive paper tape 23, the magnitude of the current being governed mainly by the energy of the cathode beam, since the resistance of each individual comb wire I2 and of the sensitized paper tape 23 may be small in comparison with that of the beam.

With the current window of this invention, the current flowing from a particular comb wire I2 through the sensitized paper 23 to the knife edge 22 will be sensibly the same whether it originates in electrons which strike the inner portion of the particular comb wire I2 close to the point at which it passes through the tube wall, at the end of the wire toward the cathode 4, or anywhere in between. Thus the stringency of the electron beam-focusing requirements are greatly reduced, with consequent simplification of the apparatus and reduction in the cost.

Aieature of :the' nventionis the utili ation of a very much larger part of the energy available in a cathode beam :than has heretofore been possible. As is well known, there is a decidedlliniit to the sharpness with which a cathode-beam may be brought to a point focus due to the fact that the electrons when brought sufiicien-tly close together tendto repelone another. However,

' 'sufiiciently spread apart in one direction, the

electron beam may be focused with almost any desireddegree ofsharpness in theother direction. That is to Say,-a linefocus maybe obtained which is far sharper than a point focus, and-far more electron current energy may be concentrated in a narrow rectangle than -couldbe concentrated in a circular spot of'the same width.

By the preferred construction in accordance with this invention advantage is taken of this fact and it is therefore preferred to employ an electron gun arrangement which is capable of focusing the electron beam into a narrow -rectanglewhose width is no greater than the Width of a single one of the comb wires 12 'but'whose length may be as great as the projected length of the same *comb wire on a plane perpendicular to the direction of motion of the oncoming-electron beam. Thus all the eleetronswhich are concentrated into the narrow rectangular 'spot strike some portion of a particular comb -wire whether close to the point at which it passes through the-tube wall or further back towardsits end; and all of these electrons combine to form a substantial current from the comb wire H! to the :knife edge 22 and-therefore make a heavy and durable impression on the sensitized tape 23. As is well known, the beam may be -focused in a narrow rectangular spot by the use of a suitably shaped aperture in the electrode which defines the cross-section of the "beam. This arrangement is shown in Figs. 11 and '2, where the electrode is shown'mounted in front of the cathode and provided with a narrow vertical slit 6. The same result may also be secured by other means, for example, the means described and claimed-in Winans application Serial 'No.30'7,255, filed December 2, 1939.

Various modifications of the arrangements above described which are within the spirit of the invention will occur to those skilled in the art. In particular, it is contemplated that the conducting comb of this invention may be constructed in a number of different ways and of a number of different materials. For example, an excellent construction is that described and claimed in Ekstrand application Serial No. 328,819 filed April 10, 1940.

What is claimed is:

1. A cathode ray device which comprises a vessel having a non-conductive wall, means within said vessel for projecting a cathodebeam, and beam-receptive means sealed into said wall in position to be impinged by said beam, said beamreceptive means comprising a plurality of discrete conductors arranged in a single row and extending parallel to each other through said wall and disposed with one of their smaller dimensions lying in the direction of the row, the outer end of each conductor terminating in a sharp tip, the distance fromeach [of said tips to an adjacent tip being of the order of 0.01 inch.

2. A cathode ray device which comprises a vessel having a non-conductive wall, means within said vessel for projecting a cathode beam, and beam-receptive means sealed into said wall in positiontobezimpinged by said beam, said beamreceptive means comprising a plurality of closely spaced ;discreteco nductors, insulated from .each other, )arranged in :a single .row and extending parallelrto eachpther through said wall, at least the portion of each of said conductors lying within said vessel beingidisposed at an oblique angle to the direction .of projection: of .said beam.

3. cathodel rayldevice which comprises a vessel havingla non-conductive wall, means within said vessel for projecting a cathode beam, and beam-receptive means sealed into said wall in position'to -be 'impinged by said beam,.said beamreceptive meanscomprising a plurality of discrete conductors, arranged in a single row, parallel to each other and spaced apart bydistances of the order of less than 0.01 inch, and extending through said wall, at leastthe portion of each of said conductors lying within said vessel being disposed at an oblique angle to the direction of projectionof said beam.

'4. Apparatus for synthesizing an image, elementbyelement, fromsignals related to the light and shade values of successive elements of an image, which comprises a vessel having .a nonconductive wall,- means within said vessel for projecting -a cathode beam, and beam-receptive means sealed into-said Wall in position to be impinged by said beam, said beam-receptive means comprising a plurality of discrete conductors arranged in a single row and extending parallel to each other through said wall and disposed with one of their smaller dimensions lying in the direction of the row, the outer end of each condue-tor terminating in ,a sharp tip, the distance from the center line of each of said conductors to the center line of an adjacent conductor being of "the order of the width of a'single image element.

5. Apparatus 'for synthesizing an image, element by element, from signals related to the light and shade values of successive elements of an image, whichcomprises a vessel having a nonconductive wall, means 'within said vessel for projecting a cathode beam, and beam-receptive means sealed-into "said wall in position to be'impinged by said beam, said beam-receptive means comprising a plurality of discrete bare conductors arranged in a single line and 7 extending parallel to each other through said wall and disposed with one of their smaller dimensions lying in the direction of the row, the outer end of each conductor terminating in a sharp tip, adjacent sides of adjacent conductors being spaced apart by distances of the order of less than the width of a single image element.

6. A cathode ray device which comprises a vessel having a non-conductive wall, means within said vessel for projecting a cathode beam having a cross-section in the form of a narrow rectangle, and beam-receptivemeans sealed into said wall in position to be impinged by said beam, said beam-receptive means comprising a plurality of closely spaced discrete conductors arranged in a single row and extending parallel to each other through said wall, at least the portion of each of said conductors which lies within said vessel being disposed at an oblique angle to the direction of projection of said beam and lying in the plane defined by the longer axis of said narrow rectangle and said projection direction.

7. A cathode ray device which comprises a vessel having a non-conductive wall, means within said vessel for projecting a cathode beam, and

beam-receptive means sealed into said wall in position to be impinged by said beam, said beamreceptive means comprising a plate of insulating material and aplurality of discrete strips of conductive material attached to the surface of said plate, said strips being spaced from each other and extending parallel to each other through said wall, at least the portion of each of said strips which lies within said vessel being disposed at an oblique angle to the direction of projection of said beam.

8. Apparatus for synthesizing an image on a sheet of electricity-sensitive material disposed adjacent said apparatus in position to receive electric current therefrom, which comprise a vessel having a non-conductive walL-means within said vessel for projecting a cathode beam, a plurality of discrete elements for collecting beam current of relatively large cross-section inside of said vessel and concentrating it to a point outside of said vessel, each of said elements comprising a conductor extending through the wall of said vessel, terminating outside of said vessel in a comparatively small area and terminating inside of said vessel in a surface of comparatively large area, said surfaces being in position to'be impinged by said cathode beam, said external ends lying in a row and having a centerto-center spacing of the order of the width of an elemental image area, and means for sweeping said cathode beam over said surfaces.

9. Apparatus for synthesizing an image on a sheet of electricity-sensitive material disposed adjacent said apparatus in position to receive electric current therefrom, which comprises a vessel having a non-conductive wall, means within said vessel for projecting a cathode beam, a plurality of closely spaced discrete elements for collecting beam current of relatively large crosssection inside of said vessel and concentrating it to a point outside of said vessel, each of said elements comprising a conductor extending through the wall of said vessel, terminating outside of said vessel in a point and terminating inside of said vessel in a surface of substantial extent, said surfaces being in position to be impinged by said cathode beam, said external end points lying in a row, and means for sweeping said cathode beam over said surfaces.

10. A cathode ray device which comprises a vessel having a non-conductive wall, means within said vessel for projecting a cathode beam, and beam-receptive means sealed into said wall in position to be impinged by said beam, said beam-receptive means comprising a plurality of discrete elongated non-overlapping conductors arranged in a single row and extending through said wall and disposed with one of their smaller dimensions lying in the direction of the row, the center-to-center spacing distance of the outer ends of said conductors being uniform and close, the cross-sectional area of the outer parts of each of said conductors being less than the square of said spacing distance, the inner part of each of said conductors presenting to said projected beam an area substantially in excess of the square ofsaid spacing distance.

11. A cathode beam device having a wall of insulating material, a target member for the beam forming a part of said wall and consisting of an insulating element sealed therein and projecting therefrom within said vessel, said element having conducting material plated on one face thereof and extending through said seal to the outside of said vessel and within said vessel in a position to be impinged by said beam.

12. A cathode beam device comprising a vessel having a wall of vitreous insulating material, a target member for the beam forming a part of said wall and consisting of a vitreous insulating element sealed therein and projecting therefrom both within and without said Vessel, said element having a face with narrow strips of conducting material plated thereon, which strips extend through said seal with their outer extremities lying close together in a row along an edge of said element in position to be aligned with and uniformly spaced from an external electrode, said strips having portions extending within the vessel for a distance many times greater than the width of a strip at said edge, and means for deflecting said beam to cause it to impinge in turn upon said strips, said beam being oblong in cross section at said target with its short transverse dimension substantially perpendi-cular to the longest dimension of each of said strips.

EDMOND BRUCE. 

